The present invention generally relates to liquid heating apparatus and, in a representatively illustrated embodiment thereof, more particularly relates to a specially designed temperature sensing side port insert for an electric water heater.
In electric water heaters having non-metallic tanks, such as plastic tanks reinforced by external, resin-impregnated filament winding, a design challenge is presented in sensing the temperature of heated water in the tank portion of the water heater for water temperature control purposes. Sensing the water temperature by simply sensing the outer side surface temperature of the tank is not a practical option due to the thermal insulating characteristics of the plastic/filament winding construction of the tank walls.
Previous alternative proposals have entailed the sealed insertion through the tank wall of a tubular metal port member through which an electric heating element extended into the tank interior, the heating element being appropriately sealed within the port member. Heat from the stored tank water was conductively transferred outwardly through the port member to an externally disposed thermostat used to appropriately activate and de-energize the heating element in response to sensed tank water temperature.
This proposed approach to sensing internal tank water temperature presented two primary problems. Depending on the configuration of the port member, it could cause an undesirable degree of temperature sensing lag, and a corresponding amount of water-set point temperature overshoot, or could alternatively cause a scale build-up between the electrical heating element and the port member which substantially shortened the operational life of the heating element. A need thus exists for an improved port member design which eliminates or at least substantially reduces these problems.